Leukocytes are the principal cell involved in host-parasite defense, and of the various types of leukocytes, the polymorphonuclear leukocyte's (PMN) role in the process is crucial. Any factor or drug that alters the PMN's responsiveness to infectious materials could compromise host-defense. Recently, by adapting the Micro ELISA technique to the study of PMN aggregation, we have demonstrated that the PMN is extremely sensitive to F-. Ten to the -9 M NaF was as effective an inducer of PMN aggregation as 1.0 Mug L.P.S. This PMN responsiveness to F- is in the order of 10 cubed to 10 to the 5 less than has been previously reported to affect PMN function. Aggregation has been related to PMN adherence to blood vessel walls (pavementing) prior to their emigration out of the vascular bed. Although the significance of our finding is unclear with respect to host-defense or pathology, the widespread use of systemic and topical F- demands better knowledge of the influence of this anion on host-defense cells than is currently available. Specifically, we will be seeking answers to the following questions: 1. How does F- induced aggregation compare with aggregation induced by other known aggregating agents? 2. What conditions optimize F- induced aggregation, and are these conditions similar to those required for optimum aggregation by other agents? 3. What biochemical systems are involved in F- induced aggregation, and are these systems similar to those evoked by other agents? 4. Does F- induce or inhibit other PMN events, and are they related to aggregation? This study should provide a knowledge base required for a better understanding of F--PMN interactions and a better understanding of the regulation of PMN functions.